1. Field of the Invention
Embodiments of the invention relate to semiconductor processing equipment. In particular, embodiments of present invention are related to batch wafer processing equipment.
2. Description of Related Art
Most semiconductor processing equipment utilizes robotics to transfer silicon wafers to specific locations within the system for conduct of processes to modify the wafer surface. One example of batch wafer processing is vertical diffusion furnaces used to form thermal oxides, diffuse in dopant layers, or deposit oxides, nitrides or other layers by chemical vapor deposition (CVD).
For most large batch processing, the product in the form of silicon wafers or other shape substrates having a diameter of 100 mm or greater, are placed into slots of a wafer carrier, sometimes called a rack or wafer boat. The wafer boat is mounted vertically on top of a heat blocking support structure (called a pedestal) which in turn sits upon a door closure assembly, referred to as the process chamber door. For most current large batch systems, the assembly to be inserted into the process chamber area consists of the door, pedestal, and wafer carrier. That stack of separable parts is moved as a unit under the open lower end of the process chamber (e.g., process tube) and then moved upward into the process chamber until the door assembly closes against a flange at the lower end of the process chamber or tube.
For higher throughput, batch systems frequently have two or even three such door, pedestal, carrier assemblies and a means for moving that stacked assembly from a load/unload position to the insertion position under the process chamber.
The desire to minimize cost and time per wafer processed in general favors the use of the largest number of parts possible per processing cycle. The batch size however, becomes constrained by overall system height and process uniformity which limits the spacing between parts which is set by the slot pitch of the wafer carrier.
Existing techniques to automate the process to allow more parts to be processed have a number of drawbacks. One technique moves the slots closer together or lengthens the wafer boat. The technique reduces the wafer boat slot pitch. Another technique increases the length of the wafer boat or boat to allow for adding additional wafer slots to accommodate a larger load size. However, this technique increases the space below the process chamber as well as the length of the process chamber.
For current system designs, the door, pedestal, and wafer boat are moved as one unit, once assembled. The requirement for space below the chamber for the door/pedestal/carrier assembly has set an upper limit on the number of parts (e.g., wafers) that can be placed in a wafer carrier (e.g., wafer boat) processed in a single cycle.